The invention relates to a rotary-wing aircraft rotor, whose blades are automatically foldable and equipped with electrical equipment, such as de-icing or anti-icing equipment, or even positioning lights or lamp(s) at the blade ends, or an electrical actuator to control a mobile member such as a blade flap, or any other electrical equipment requiring the routing of electrical energy to the blades from an electrical collector placed at the center of the hub of the rotor. This routing of electrical energy is provided by an electrical connection installation, essentially comprising an electrical harness comprising, for each blade, at least one electrical connecting cable, tied to a member for linking the corresponding blade to the hub of the rotor, and provided at its ends with connectors to ensure an electrical connection between the collector and the blade.
More precisely, the invention relates to a rotary-wing aircraft rotor, in particular a helicopter main rotor, of the type known in particular by EP-0 754 623 and FR 2 781 198 and comprising:
a hub, designed to be driven in rotation about an axis of the hub which is the axis of rotation of the rotor,
at least two blades, each of which is connected to the hub by a link member that is substantially radial with respect to the axis of rotation, each blade being firmly connected by its root to a folding mount, mounted in a pivoting manner at a radially outer end of the said link member, about an axis for folding the said blade between two positions, one of which is a flight position, in which the said mount is attached to the said link member in such a way that the said blade is substantially aligned in the projection of the said link member, and the other of which is a position folded along one side of the rotary-wing aircraft, in which the said mount and blade are pivoted about the said folding axis on one side of the said link member, and
an electrical connection installation comprising, for each blade, at least one electrical connecting cable connecting a first connector, carried by the hub and electrically connected on the latter, to a second connector on the blade and connected to at least one electrical device of the said blade.
On a rotor according to EP 0 754 623, the connecting cable, for each automatically foldable blade, comprises (see FIGS. 7 and 13) a first section, radially towards the outside, arranged like an overhead hook and extending from this blade to the corresponding link member, and connecting the second connector on this blade to a rotating part, with which this first section is integral in rotation, of a rotating connector coaxial with the folding spindle about an extension of this spindle, and whose fixed part is connected, mechanically and electrically, to a first end, in a radially outer position, of a second section of connecting cable, held substantially radially on this link member. This overhead hook of the connecting cable has a rounded cross section, possibly an armoured structure, and is connected to the second connector, which is itself connected to the electrical equipment, for example de-icing or anti-icing equipment of this blade, and when an actuator housed in the corresponding link member commands the pivoting of the mount with the blade about the folding spindle, this first section of cable rotates with the rotating part of the rotating connector about this same spindle, at the same time as the blade, which makes any intervention on the second connector useless.
However, during the foldings of the blade, the pivoting of the blade with the mount with respect to the corresponding link member can introduce tensions that can cause damage in the overhead hook and on the rotating part of the rotating connector and also on the second connector, and such a rotating connector is furthermore a relatively complex, costly and fragile component.
In fact, it is not recommended to give this overhead hook a length sufficient to allow the complete folding of the blade whilst guaranteeing the absence of tensions, because an overhead hook of such length would have large forces applied to it and would be subjected to ample flutter movements, favouring its catching on or an unwanted collision with adjacent components, such as blade root pendular anti-vibration devices, aerodynamic dome, sleeve or drag dampers, on a rotor in rotation, on which the corresponding blade carries out angular deflections in pitch, flapping and drag.
FR 2 781 198 proposes improvements to rotors with automatically foldable blades and an electrical de-icing installation according to EP 0 754 623, in particular for avoiding the use of rotating connectors and reducing the stresses and/or displacements of the connecting cable in its overhead hook section connecting the link member to the second connector on the blade, when the rotor is rotating and during the operations of folding and unfolding the blades.
For this purpose, according to FR 2 781 198 (see FIGS. 3 and 4), an elongated part of this overhead hook, of substantially flattened rectangular cross section, whose biggest dimension is oriented substantially parallel with the axis of rotation of the rotor, is held in a member, mounted in a fixed manner or pivoting about the folding spindle, in the substantially axial projection of this folding spindle, and arranged as a fork in which the said elongated part of flattened cross section is engaged and held by at least one elastic tab. This retaining fork prevents the displacements of the overhead hook on either side of the folding spindle, during a blade""s folding or unfolding, which prevents torsions harmful to this section of connecting cable, and is much more simple, economical and reliable than a rotating connector.
But the flattened rectangular cross section of this overhead hook section of cable above the link between the blade root and the link member favours a longitudinal slipping of the section of cable in the fork during the folding of the blade, and in particular generates a large aerodynamic drag, which causes a disturbing slipstream phenomenon. Furthermore, considering the angular movements, in particular of flapping and pitch combined, of this section of cable and of its mechanical link with the link member, when that latter and the blade are carrying out these angular movements, it has proved necessary to form recesses in the periphery of a profiled dome covering the rotor head, and this amplifies the said slipstream phenomenon.
The basic problem for the invention is to overcome these disadvantages whilst avoiding the use of rotating connectors, and avoiding the formation of a disturbing slipstream, caused by recesses in the profiled dome surmounting the rotor head and by a section of connecting cable with a flat profile oriented substantially parallel with the axis of the rotor.
For this purpose, the rotary-wing aircraft rotor according to the invention, of the type described above, is characterized in that the connecting cable comprises a first flexible section, of essentially cylindrical shape with a rounded cross section, preferably substantially circular, connecting the said second connector to a second section, held on the corresponding link member, of the said connecting cable, whose first section comprises a held part which, in all the positions of the blade about the folding spindle, is maintained fixed on a cable support tied to the said folding spindle, such that the said held part is maintained above the said mount and the said radially outer end of the said link member, in an off-centered position with respect to the said folding spindle and substantially on the folding side of the said blade, in order that the folding of the blade by pivoting about the said folding spindle causes the first section of cable to curve and to move naturally in order to accommodate itself to the said folding without extension of the said first section of cable.
The rounded shape of the cross section of the first section of cable sets up only a limited aerodynamic drag and allows, at the level of the connection with the second section of cable, a fixing much closer to the link member, such that it is no longer necessary to form recesses in a protective dome of the rotor head, or at the very least the dimensions of these recesses are limited to the minimum. Furthermore, no matter on which side of the helicopter the folding of a blade is carried out, the first section of connecting cable is held, in all blade configurations, by its part held on a point of the cable support which is not in the projection of the folding spindle, but offset with respect to the latter on the folding side, such that during the folding and unfolding of the blade the first section of cable can deform naturally without extension, and in particular can curve and move in such a way as to accompany the blade during its rotation without applying damaging tension to the second connector or to the rest of the connecting cable.
According to an advantageous, simple, economical and easily removable arrangement, the held part of the said first section of cable is held in a cradle, formed in the said cable support, by at least one collar fixed to at least one side of the cradle and brought down in the closed position onto the opposite side of the cradle, to which the collar is fixed, preferably in a detachable manner, by at least one fixing element in a position of maintaining the said held part between the cradle and the collar.
Advantageously, the cable support comprises a support arm, tied to the said folding spindle, and extending in a substantially radially protruding manner with respect to the said folding spindle and on the folding side of the said blade.
This support arm can be mounted in a fixed or pivoting manner on the folding spindle and, for this purpose, the cable support advantageously also comprises a support spindle, upon which the support arm is mounted in cantilever manner and which is itself mounted substantially coaxially at the end of the folding spindle, and held in a substantially axial direction with respect to the latter, by at least one holding member.
As a variant, at least the support arm is integrated with the first section of cable, at the level of the held part, and protruding laterally from this first section of cable, and the support arm is tied to the folding spindle, for example by the intermediary of the support spindle on which the support arm is mounted in cantilever manner.
When the automatic folding apparatus of each blade is such that at least the upper end of the folding spindle is tubular, as known from FR 2 742 726, it is then advantageous for the support spindle to be partly engaged axially and held, at least axially, inside the upper tubular end of the folding spindle.
In order to reduce the bulk of the cradle and of the collar, the cradle is preferably formed in the lower face of the said support arm, and the collar is disposed between the upper face of the radially outer end of the said link member and the said lower face of the said support arm against which the said collar is fixed.
Furthermore, the held part of the first section of cable can be advantageously delimited by at least one radial excess thickness of the said first section, preferably formed by over-moulding its outer cover, and preventing longitudinal sliding of the said held part with respect to the cradle and the collar.
Also advantageously, as known from EP 0 754 623 and FR 2 781 198, and for the reasons given in these two documents, the second section of cable has an elongated part of substantially flattened rectangular cross section, maintained substantially flat on the top of the said link member, that is to say such that the largest dimension of its cross section is oriented substantially perpendicular to the axis of the rotor, in particular in order to facilitate the fixing of this second section of cable on the link member, to reduce the aerodynamic drag and to attenuate the mechanical forces applied to this section of cable, which preferably furthermore extends in a direction laterally inclined with respect to the longitudinal axis of the said link member, on the folding side of the blade, in order to facilitate the connection of the first section of cable, to limit the length of the latter and to make its installation more favourable between the link member and the second connector.
Thus, the rotor according to the invention can also benefit from the advantages resulting from the use of other features of the electrical connection installation according to EP 0 754 623 and FR 2 781 198, to which reference can be made for more details, and whose descriptions are incorporated in the present description by way of reference.
In particular, the second section of cable can be advantageously connected to the first connector on the hub by the intermediary of a third section of the connecting cable, the said third section comprising an overhead hook, in the shape of a flattened half-loop, of substantially flattened rectangular cross section whose largest dimension is substantially perpendicular to the axis of rotation, and whose concavity is facing substantially towards holding and articulation means connecting the corresponding link member to the hub, and substantially radially towards the axis of rotation, the said overhead hook being thus deformable in flexion and torsion in order to accommodate itself to the angular deflections in pitch, drag and flapping of the blade and of its link member with respect to the hub, as known from the two documents mentioned above.
Similarly, the second section of cable can advantageously be connected to the overhead hook of the third section of cable by a joint connected to the link member by a link which is articulated at least in pivoting manner about an axis substantially parallel with or slightly inclined with respect to the longitudinal pitch change axis of the link member and of the blade, in order to attenuate the mechanical forces applied to the connecting cable whilst allowing a good take-up of the forces applied to the latter when the rotor rotates and the corresponding blade is carrying out its angular deflections in pitch, flapping and drag, as proposed in FR 2 781 198.